A large earthquake off the coast of south-central Chile in 1737 may have caused a substantial tsunami that was absent from historical records. Historical records are used to predict how often tsunamis are likely to occur in a region in the future. Until now, it was previously believed that tsunami-causing earthquakes had occurred in this area of Chile three times since the 1570s, including after the magnitude 9.5 earthquake of 1960. However, this discovery of an unrecorded tsunami means that tsunamis may have struck the Chilean coast more frequently than previously believed. This means the average time between historical tsunami occurrences could be significantly reduced, to an average of 130 years.